Abstract:

In this paper we present a rigid-rod model (involving a restricted set of orientations) which is solved first with mean-field theory and then by Monte Carlo simulation. It is shown that both interparticle attractions and anisotropic adsorption energies are necessary in order for two successive fluid-fluid transitions to occur. The first is basically a gas-liquid condensation of ‘‘lying down’’ rods in the plane of the surface, and the second involves a ‘‘standing up’’ of the particles. A close qualitative correspondence is established between the results obtained in the mean-field and Monte Carlo descriptions. The role of biaxial states, i.e., in-plane orientational ordering, is also discussed in both contexts. To this end, we develop an analogy between our one-component rod monolayer and a bidisperse system of interconverting isotropic particles.